"The multiverse is no longer a model, it is a consequence of our models.”

~Aurelien Barrau, particle physicist at CERN

The Hollywood blockbuster, The Golden Compass, adapted from the first volume of Pullman's classic sci-fi trilogy, "His Dark Materials" portrays various universes as only one reality among many, but how realistic is this kind of classic sci-fi plot? While it hasn’t been proven yet, many highly respected and credible scientists are now saying there’s reason to believe that parallel dimensions could very well be more than figments of our imaginations.

"The idea of multiple universes is more than a fantastic invention—it
appears naturally within several scientific theories, and deserves to
be taken seriously," stated Aurelien Barrau, a French particle
physicist at the European Organization for Nuclear Research (CERN).

There are a variety of competing theories based on the idea of parallel
universes, but the most basic idea is that if the universe is infinite,
then everything that could possibly occur has happened, is happening,
or will happen.

According to quantum mechanics, nothing at the subatomic scale can
really be said to exist until it is observed. Until then, particles
occupy uncertain "superposition" states, in which they can have
simultaneous "up" and "down" spins, or appear to be in different places
at the same time. The mere act of observing somehow appears to "nail
down" a particular state of reality. Scientists don’t yet have a
perfect explanation for how it occurs, but that hasn’t changed the fact
that the phenomenon does occur.

Unobserved particles are described by "wave functions" representing a
set of multiple "probable" states. When an observer makes a
measurement, the particle then settles down into one of these multiple
options, which is somewhat how the multiple universe theory can be
explained.

The existence of such a parallel universe "does not even assume
speculative modern physics, merely that space is infinite and rather
uniformly filled with matter as indicated by recent astronomical
observations," Max Tegmark, a cosmologist at MIT in Boston,
Massachusetts concluded in a study of parallel universes published by
Cambridge University.

Mathematician Hugh Everett published landmark paper in 1957 while still
a graduate student at Princeton University. In this paper he showed how
quantum theory predicts that a single classical reality will gradually
split into separate, but simultaneously existing realms.

"This is simply a way of trusting strictly the fundamental equations of
quantum mechanics," says Barrau. "The worlds are not spatially
separated, but exist as kinds of 'parallel' universes."

Partly because the idea is so uncomfortably strange, it’s dismissed as
sci-fi by many critics. But there are also many credible, respected
proponents of the theory—a group that is continuously gaining new
adherents as new research unveils new evidence. Some Oxford
research—for the first time—recently found a mathematical answer that
sweeps away one of the key objections to the controversial idea. Their
research shows that Everett was indeed on the right track when he came
up with his multiverse theory. The Oxford team, led by Dr David
Deutsch, showed mathematically that the bush-like branching structure
created by the universe splitting into parallel versions of itself can
explain the probabilistic nature of quantum outcomes.

The work has another strange implication. The idea of parallel
universes would apparently side-step one of the key complaints with
time travel. Every since it was given serious credibility in 1949 by
the great logician Kurt Godel, many eminent physicists have argued
against time travel because it undermines ideas of cause and effect. An
example would be the famous “grandfather paradox” where a time traveler
goes back to kill his grandfather so that he is never born in the first
place.

But if parallel worlds do exist, there is a way around these
troublesome paradoxes. Deutsch argues that time travel shifts happen
between different branches of reality. The mathematical breakthrough
bolsters his claim that quantum theory does not forbid time travel. "It
does sidestep it. You go into another universe," he said. But he admits
that there will be a lot of work to do before we can manipulate
space-time in a way that makes “hops” possible. While it may sound
fanciful, Deutsch says that scientific research is continually making
the theory more believable.

"Many sci-fi authors suggested time travel paradoxes would be solved by
parallel universes but in my work, that conclusion is deduced from
quantum theory itself."

The borderline between physics and metaphysics is not defined by
whether an entity can be observed, but whether it is testable, insists
Tegmark.

He points to phenomena such as black holes, curved space, the slowing
of time at high speeds, even a round Earth, which were all once
rejected as scientific heresy before being proven through
experimentation, even though some remain beyond the grasp of
observation. It is likely, Tegmark concludes that multiverse models
grounded in modern physics will eventually be empirically testable,
predictive and disprovable.

Somewhere there's a universe where everyone on here has a billion dollars / or the equivalent in pounds, yen, marks, we have flying cars powered by veggie oil, there are trips to Mars, Jupiter, Saturn, skiing on Europa, vacations to various points in time, & I meet a supermodel !!!
& somewhere in Florida, Jeb Bushis eating a live puppy....

Seriously, these universes could be by - products of actions in THIS universe - If someone squashes a butterfly in this universe, it has an effect in an alternate universe.

but does time really exist? if there really are other dimensions where everything has happend, is happening, or will happen, does time even matter? could this universe in which we exist be but a speck of dirt floating in the bath tub of a higher being? or be a speck of dirt on a speck of dirt on a speck of dirt on a speck of...

i don't think the universe we inhabit is infinite and that there is an "edge" to it. if we broke through that barrier would it be like bursting a bubble? what's on the other side?

If (and it's a mighty big 'if') there are an infinity of parallel universes, there must be one where we can move easily between it and other universes, but also another one which exists in reality all by itself with no other parallel neighbour. The mechanics of the Big Bang dictate that Dark Energy (expanding the universe) will be overcome by Gravity (contracting the universe) and everything will be renewed in another Big Bang.

Some " experts " are of the opinion that alternative universes & variations of same may account for phenomena like " ghost " sightings / hauntings & UFO's, etc. The fabric of our space becames so thin that alternate universes get a glimpse into each other. It's only a theory, but it's a very interesting one & would explain some things.